Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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000 FXUS64 KMRX 080925 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 425 AM EST Fri Dec 8 2017 .SHORT TERM...
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(Today and Tonight)...Very challenging forecast for the short term. Models in overall agreement that an approaching upper trough along with a developing surface low near the east coast will bring some precipitation to at least eastern parts of our area. While upper jet dynamics bring some lift to the area, models disagree on available moisture and how far west the significant precipitation will make it. GFS looks to be an outlier in how aggressive it is for our area, so plan to lean more toward the NAM/SREF/ECMWF solutions. It will be cold enough aloft for all snow in the higher terrain, and precip amounts are expected to be enough for the winter weather advisory to be expanded to the northeast TN mountain zones. Will also spread PoPs further west into the valley, but precipitation amounts should be light and will keep PoPs fairly low. Rain may mix in with snow in some of the lower elevation areas as well since boundary layer temps expected to be borderline for snow. .LONG TERM...(Saturday through Thursday)...This period should be another chilly one with approximately three short waves or "clippers" rotating southeast around a seemingly permanent upper level low over Quebec. The first moves across the forecast area during the period Saturday afternoon through early Sunday morning generating some orographic snow showers in the higher terrain across Southwest Virginia and Northeast Tennessee with a few flurries in the valleys in these areas. Due to limited moisture, snowfall amounts look to be around a half to one inch in these higher terrain areas into Sunday morning. Sunday afternoon through the daytime period Monday will be a dry period while the region awaits the next clipper which impacts the area from about Monday night through Tuesday night. This system looks like it will produce a few more orographic snow showers in the higher terrain of Southwest Virginia, Northeast Tennessee and the Smoky Mountains of Central East Tennessee with moisture limitations keeping amounts around an inch or less, along with a few flurries in the valleys, generally north of interstate 40. Wednesday should be another dry day with the final clipper building southeast across the forecast area later Wednesday night through Thursday night. This system is modeled to have a little more moisture associated with it, generating perhaps one to two inches of snow in the higher terrain. However, due to the fact that this feature is about a week away, forecast uncertainty is a bit higher. Concerning the temperature forecast, max and mins will be around ten to as many as fifteen degrees below normal for mid December, with slightly warmer maxes on Monday and again on Thursday, due to winds shifting to a west to southwesterly direction ahead of each short wave.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 38 27 43 24 / 30 20 0 0 Knoxville McGhee Tyson Airport, TN 37 28 40 22 / 30 20 10 0 Oak Ridge, TN 38 26 40 22 / 20 10 10 0 Tri Cities Airport, TN 37 28 37 18 / 30 30 10 20
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&& .MRX WATCHES/WARNINGS/ADVISORIES...
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NC...Winter Weather Advisory until 7 AM EST Saturday for Cherokee- Clay. TN...Winter Weather Advisory from 7 AM this morning to 7 AM EST Saturday for Johnson-Southeast Carter-Southeast Greene- Unicoi. Winter Weather Advisory until 7 AM EST Saturday for Blount Smoky Mountains-Cocke Smoky Mountains-East Polk-Sevier Smoky Mountains-Southeast Monroe. VA...None.
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&& $$

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